The basic concept of the dependency injection (also known as Inversion of Control pattern) is that you do not create your objects but describe how they should be created. You don’t directly connect your components and services together in code but describe which services are needed by which components in a configuration file. A container (in the case of the Spring framework, the IOC container) is then responsible for hooking it all up.

i.e., Applying IoC, objects are given their dependencies at creation time by some external entity that coordinates each object in the system. That is, dependencies are injected into objects. So, IoC means an inversion of responsibility with regard to how an object obtains references to collaborating objects.

Example:

Lets we have two classes-Car and Engine.Car has a object of Engine.

Normal way:

There are many ways to instantiate a object. A simple and common way is with new operator.

so here Car class contain object of Engine and we have it instantiated using new operator.

Without DI

With help of Dependency Injection:

Now we outsource instantiation and supply job of instantiating to third party.Car needs object of Engine to operate but it outsources that job to some third party. The designated third party, decides the moment of instantiation and the type to use to create the instance. The dependency between class Car and class Engine is injected by a third party. Whole of this agreement involves some configuration information too. This whole process is called dependency injection.

With DI

How this whole dependency injection works,we will see it in further posts.

it s simple to understand. i was checking thru various websites but cudnt understand them.. hav to learn springs in a day for simple projects… thanks a lot fr making a simple way for learning concepts..